Vehicles with an Internal Combustion Engine (ICE) are equipped with a treatment system for reducing the toxicity of the exhaust gas from the engine. The treatment system typically includes a main catalytic converter, which includes a main catalyst that reduces nitrogen oxides in the exhaust gas to nitrogen and carbon dioxide or water, as well as oxidizes carbon monoxide (CO) and unburnt hydrocarbons (HCs) to carbon dioxide and water. However, the main catalyst must be heated to a light-off temperature of the main catalyst before the main catalyst becomes operational. Accordingly, the exhaust gas must heat the main catalyst to the light-off temperature of the main catalyst before the reaction between the main catalyst and the exhaust gas begins. The majority of the pollutants, particularly the majority of the CO and HCs emitted during the operation of the engine, occur prior to the main catalyst reaching the light-off temperature.
In order to speed the heating of the main catalyst to the light-off temperature and reduce the pollutants emitted prior to the main catalyst reaching the light-off temperature, the exhaust gas treatment system may include a light-off catalyst that is disposed upstream of the main catalyst. The light-off catalyst, due to a high Platinum Group Metal (PGM) content, readily promotes exothermic reactions, such as the oxidation of the CO and HCs to generate additional heat, which is transferred to the main catalyst to reduce the time to heat the main catalyst to the light-off temperature.
Additionally, some vehicles may include an exhaust gas heater, such as but not limited to an electric heater, to further heat the exhaust gas to reduce the time to heat the main catalyst to the light-off temperature. In conventional vehicles that are only powered by the ICE, the exhaust gas heater is limited to heating the exhaust gas only after the engine is started, i.e., post crank heating. In hybrid vehicles that further include an ICE/electric motor combination for powering the vehicle, the hybrid vehicle may power the exhaust gas heater with a battery prior to starting the engine, i.e., pre-crank heating, thereby further increasing the amount of heat supplied to the exhaust gas heater and reducing the time to heat the main catalyst to the light-off temperature once the engine is started.